Art of cracking hydrocarbon oils



Orig'inal Filed May 21, 1927 Edward Wfso/rz INVENTOR ATTORNEYS ReissuedSept. 8, 1936 UNITED STATES PATENT OFFICE Edward W. Isom, Scarsdale, N.Y., assignor to Sinclair Refining Company, New York, N. Y., a

corporation of Maine Original No. 1,708,180, dated April 9, 1929, SerialNo. 193,193, May 21, 1927.

Application for reissue June 30, 1931, Serial No. 548,013

GClaims.

This invention relates to improvements in the cracking of heavier andhigher boiling hydrocarbon oils, such as kerosene, gas oil, fuel oil orresidues, to produce lighter and lower boiling hydrocarbon oils such asgasoline or gasolinecontaining cracked distillates, therefrom. Thisapplication is in part a continuation of my prior application filedAugust 28, 1922, Serial No. 584,711.

In carrying out the present invention, a body of oil to be cracked ismaintained at a cracking temperature by circulating oil from this bodythrough heating tubes and back to the body and heating the oil to acracking temperature in the heating tubes, vapors are taken off fromthis body of oil and subjected to a refluxing operation, refiuxcondensate from this refluxing operation is forced once through aseparate heating conduit in which it is heated to a crackingtemperature, and the hot oil products from this heating conduit aredischarged into the body of oil first mentioned. Before the vapors aresubjected to the refluxing operation from which reflux condensate isreturned to this separate heating conduit, they may be subjected toanother refluxing operation from which reflux condensate is returneddirectly to the body of oil, heavier reflux condensate thus beingreturned to the body of oil and lighter reflux condensate supplied tothe separate heating conduit. The oil forced through the separateheating conduit is advantageously heated to a higher crackingtemperature therein than is the oil body first mentioned. Relativelyrefractory stocks, such as refiux condensate or lighter refluxcondensate, may thus be subjected to more severe cracking conditions inthe heating conduit. Fresh oil may be supplied to the body of oil firstmentioned during the operation, and additional fresh oil may be forcedthrough the separate heating conduit together with the reflux condensatesupplied thereto. In the treatment of difierent charging stocks some ofwhich are relatively more refractory than others, in carrying out thepresent invention, relatively less refractory stock is supplied directlyto the body of oil first mentioned and relatively more refractory stockis supplied to the separate heating conduit. The operation may becarried out in a continuous manner by continuously discharging tar orpitch-laden oil from the body of oil first mentioned.

In one way of carrying out the invention, the cracking operation carriedout in the separate heatingcondult is a vapor phase cracking operation.In the separate heating conduit, in this method of operation, the oil isvaporized substantially completely and the vapors are heated to a highcracking temperature. The body of oil first mentioned is maintained at alower cracking temperature so that the temperature of the hot oilproducts from the vapor phase cracking operation is reduced as they aredischarged into the body of oil. Undesirable reactions are thus arrestedand objectionable overcracking usually incident to vapor phase operationmay thus be avoided. The oil supplied to the separate heating conduitmay thus be heated in vapor phase to a high cracking temperature for arelatively short time, the desired cracking eifected and the crackedproducts then discharged into a body of oil where they are furthersubjected to the cracking conditions maintained therein but whichcracking conditions are relatively mild.

The invention will be further described in connection with theaccompanying drawing which illustrates, in a diagrammatic andconventional manner, in elevation and partly in section, an apparatusadapted for the practice of the process of the invention. but it isintended and will be understood that this further description and i1-lustration are for the purpose of exemplification and that the inventionis not limited thereto.

Referring to the drawing, a body of oil 4 is 'maintained in the shell ordrum 55. This oil is circulated in a. closed circuit from the shell ordrum 55 through the battery of heating tubes 5 and back to the shell ordrum by means of the circulating connections 8, 9 and III which includethe circulating pump I. The shell or drum 55, for example, may bemaintained about two-thirds full of oil and circulation of this body ofoil maintained through connections 8 and 9 to the heating tubes,upwardly through the heating tubes and back to the shell or drum throughconnection In. The heating tubes 5 are arranged in a suitable furnace 6.To reduce vaporization of this body of oil, particularly of heaviercomponents thereof, the shell or drum 55 is maintained undersuperatmospheric pressure. Vapors are taken off from the shell or drumthrough connection ll, passed through reflux condenser l2, vaporsremaining uncondensed therein passed to reflux condenser l6 throughconnection l5, and vapors remaining uncondensed in reflux condenser Itpassed to a condenser (not shown) in which the cracked product iscondensed through connection IT. The final condenser may be of anyordinary construction, and is connected to a receiver of ordinaryconstruction adapted to provide for separation of uncondensed vapors andgases from the condensed product. The pressure on the vapors may bereduced and regulated by a valve 12 in connection I I or by valve 13 inconnection I! or by suitable valves arranged beyond the condenser orreceiver. Superatmospheric pressure may thus be maintained in the shellor drum 55 and the reflux condensers l2 and i6 may thus be operated atthe same superatmospheric pressure or substantially at atmosphericpressure or at an intermediate pressure. Similarly, the pressure in thesystem may be maintained through the final condenser, or the finalcondenser may be operated substantially at atmospheric pressure or at anintermediate pressure.

The cooling and the refluxing of the vapors passing through the refluxcondensers i2 and I5 may be promoted or eflected by passing fresh oil tobe supplied to the operation in indirect heat exchanging relationtherewith, for example, or this cooling and refluxing may be effected bysome extraneous cooling medium. In one advantageous method of operation,fresh oil, particularly less refractory fresh oil, supplied from tank 24through connection 36 including meter 31 by means of pump is passedfirst in indirect heat exchanging relation with the vapors in the secondrefluxing operation, then, through connection 39, in indirect heatexchanging relation with the vapors in the first refluxing operation,and then, through connection 40, introduced into the circulating body ofoil. A check valve M is provided to prevent reverse flow throughconnection and a valve 42 is provided for controlling the operation.Reflux condensate from the first refluxing operation, that carried outin reflux condenser I2, is discharged through connection l3, and in oneadvantageous method of operation is returned to the circulating body ofoil through connection l4. This connection is advantageously arranged asillustrated to provide for circulation of the returned reflux condensateagain through the heating tubes 5 before it is again permitted to escapefrom the shell or drum 55 as. vapors. Part of the reflux condensate fromreflux condenser I2 may be discharged to the tank I9. Valves l4 and 15are provided for directing the flow of this reflux condensate and. forcontrolling the operation in this respect. Reflux condensate from thesecond refluxing operation, that carried out in reflux condenser ii, isdischarged to the tank 19 through connection 18. The lighter refluxcondensate collecting in tank iii if returned to the circulating body ofoil 4, tends to vaporize therefrom without substantial cracking thusutilizing heat for vaporization of these components which in the presentinvention is made available, at least in large part, for useful crackingof the oil. At the same time, the present invention provides anadvantageous method for further treatment and cracking of this morerefractory reflux condensate.

This reflux condensate is forced from the tank ll, throrgh connections20, 49 and 22, by means of pump 2|, once through the heating conduit 23.This separate heating conduit is arranged in a furnace 24 in which hotproducts of combustion from the burner 29 pass over the heating tubesmaking up the heating conduit, the waste heating gases escaping throughstack flue 80. To assist in maintaining uniform furnace conditions, apart of the heating gases may be recirculated from near the stack flueand admixed with the fresh hot products of combustion passing over theheating conduit. A return flue for this purpose is shown at 3|. Thisreturn flue may be provided with a steam injector, as illustrated, orwith other suitable forcing means for effecting recirculation of part ofthe heating gases. The hot oil products from the heating conduit 23 passthrough connections 25 and 21 to the perforated pipe 23 through whichthey are discharged into the body of oil maintained in the shell or drum55. Where the cracking operation in the heating conduit 23 is carriedout in the vapor phase, a tar separator 26 is with advantage included inthe discharge connections. A check valve 32 to prevent reverse flow anda valve 33 for regulating and controlling the operation are alsoprovided in the discharge connections from the heating conduit. Asuperatmospheric pressure in excess of that prevailing in the shell ordrum 55 may be maintained in the heating conduit 23 by means of thevalve 33, or the pressure at the discharge end of the separate heatingconduit maybe maintained at a value just sufficient to force the hot oilproducts therefrom into the body of oil in the shell or drum 55. Inaddition to the reflux condensate from tank I9, additional fresh oil,particularly more refractory fresh oil, may be forcecl through theheating conduit 23 in admixture with the reflux condensate by means ofpump 2 I. This additional fresh oil may be supplied from tank 44 throughconnection 45 including meter 45 and check valve 41 to prevent reverseflow. Valves 48 and 50 are provided for controlling the supply of refluxcondensate and such additional fresh oil to the pump 2|. In place ofsuch a single pump, separate pumps may be employed for supplying freshoil and reflux condensate from tank 44 and tank I 9 to the heatingconduit 23.,

A connection for discharging tar, or pitch-laden oil, from the shell ordrum is shown at 61. The operation in the shell or drum 55 can becarried out in a continuous manner by continuously discharging tarthrough connection 61. At the end of an operation, the charge of oiltherein may be reduced to a. heavy flux or residue and this flux orresidue. pumped out when the operation is discontinued. Connection 5| isprovided for pumping out this part of the still system at the end of anoperation.

In carrying out the present invention, stocks of different character aresubjected to cracking conditions of special advantage with reference tothe particular stock treated. Relatively more severe cracking conditionsare maintained in the heating conduit 23 than in the circulating body ofoil 4. Inone way of carrying out the invention, the oil forced throughthe heating conduit 23 is heated to a high cracking temperature in thevapor phase therein. More refractory stocks are advantageously subjectedto more severe cracking conditions in the heating conduit 23 while lessrefractory stocks are advantageously subjected to less severe crackingconditions in the shell or drum 55. The body of oil 4 is heated in aparticularlyadvantageous manner by circulation through the heating tubes5, and with this heating by maintaining a relatively high pressure onthe drum or shell 55 stocks which are less refractory but whichnevertheless are with advantage subjected to relatively high crackingtemperatures may be subjected to particularly appropriate treatment inthis part of the operation. Likewise, this invention provides for theadvantageous separation-of heavy anelintermediate components refluxedfrom the vapors taken ofl from the combined operation and forthe returnof these separate reflux condensates to that part of the operation inwhich they are subjected to the-most appropriate treatment. Lessrefractory products of the combined operation may be returned directlyto the circulating body of oil 4 while more refractory intermediatecomponents produced by the combined cracking operation or vaporized fromthe fresh oil are supplied to the heating conduit 23 where they aresubjected to relatively more severe cracking conditions.

For the production of gasoline or motor fuel components, to illustrate,the temperature of the oil body 4 may be maintained in the neighborhoodof 750 to 800 F. and the temperature of the hot oil products as they aredischarged from the heating conduit 23 may be maintained in theneighborhood of 1000 to 1200 F. Gas oil, or heavy gas oil, or fuel oil,may be supplied directly to the body of oil 4. Light gas oil or keroseneor the bottoms from the redistillation of cracked distillates for theseparation of gasoline components may be supplied to the heating conduit23 together with the reflux condensate supplied thereto. The refluxcondensate from the first refluxing operation may be returned directlyto the body of oil 4 where it is of a less refractory character or thisreflux condensate may be supplied to the heating conduit 23 where it isof a more refractory character. The heating of the tubes 5 is regulatedto avoid excessive formation of pitch or carbon. The concentration ofpitch in the body of oil I may also be regulated by dischargingpitch-laden oil therefrom and regulating the rate at which 011 issupplied thereto and at which such pitch-laden oil is discharged. Thepressure in the shell or drum 55 may be maintained in the neighborhoodof from to pounds per square inch, for example, or higher pressures maybe used with advantage. Oil may be supplied to the heating conduit 23under pressure just sufficient to effect the discharge of the hot oilproducts therefrom into the body of oil I, or higher pressures may beused and the pressure reduced, for example, at valve 33. The hot oilproducts discharged from the separate heating conduit into the body ofoil 4 assist in heating this body of oil and also assist in maintaininguniform the conditions throughout the body of oil by the agitationprovided. The heat supplied to the body of oil by the hot oil productsdischarged from the separate heating conduit is supplied internally, ina particularly advantageous manner, and to this extent reduces theamount of external heating required or increases the capacity of theapparatus.

I claim:

1. A method of cracking hydrocarbon oils, comprising maintaining a bodyof oil ata cracking temperature by circulating oil from said bodythrough heating tubes and back to the said body and heating the oil to acracking temperature in said heating tubes, taking off vapors from saidbody of oil and subjecting them successively to a first and a secondrefluxing operation, returning reflux condensate from the firstrefluxing operation to said body of oil, forcing reflux condensate fromthe second refluxing operation once through a separate heating conduitand heating it therein to a cracking temperature, and discharging hotoil products from said heating conduit into said body of oil.

2. A method of cracking hydrocarbon oils, comprising maintaining a bodyof oil at a cracking temperature by circulating oil from said bodythrough heating tubes and back to said body and heating the oil to acracking temperature in said heating tubes, supplying relatively lessrefractory oil to said body of oil, taking oif vapors from said body ofoil and subjecting them successively to a first and a second refluxingoperation, returning reflux condensate from the first refluxingoperation to said body of oil, forcing reflux condensate from the secondrefluxing operation together with additional relatively more refractoryoil once through a separate heating conduit and heating the mixturetherein to a higher cracking temperature, and discharging hot oilproducts from said heating conduit into said body of oil.

3. A method of cracking hydrocarbon oils, comprising maintaining a bodyof oil at a cracking temperature by circulating oil from said bodythrough heating tubes and back to said body and heating the oil to acracking temperature in said heating tubes, taking off vapors from saidbody of oil and subjecting them successively to a flrst and secondrefluxing operation, returning reflux condensate from the firstrefluxing operation to the oil circulating from said body of oil to saidheating tubes, forcing reflux condensate from the second refluxingoperation once through a separate heating conduit and heating it thereinto a cracking temperature, and discharging hot oil products from saidheating conduit into said body of oil.

4. A method of cracking hydrocarbon oils, comprising maintaining a bodyof oil at a cracking temperature by circulating oil from said bodythrough heating tubes and back to said body and heating the oil to acracking temperature in said heating tubes, taking off vapors from saidbody of oil and subjecting them successively to a first and a secondrefluxing operation, returning reflux condensate from the flrstrefluxing operation to the oil circulating from said body of oil to saidheating tubes, forcing reflux condensate from the second refluxingoperation together with fresh oil once through a separate heatingconduit and heating the mixture therein to a cracking temperature, anddischarging hot oil products from said heating conduit into said body ofoil.

5. A method of cracking hydrocarbon oils, comprising maintaining a bodyof oil at a cracking temperature by circulating oil from said bodythrough heating tubes and back to said body and heating the oil to acracking temperature in said heating tubes, taking off vapors from saidbody of oil and subjecting them successivel to a first and a secondrefluxing operation, returning reflux condensate from the firstrefluxing operation to said body of oil, forcing reflux condensate fromthe second refluxing operation together with relatively more refractoryoil once through a separate heating conduit and heating the mixturetherein to a higher cracking temperature, discharging hot oil productsfrom said heating conduit into said body of oil, passing relatively lessrefractory oil in heat exchanging relation with the vapors in at leastone of said refluxing operations and supplying said relatively lessrefractory oil preheated by said heat exchange to said body of oil.

6. A hydrocarbon oil cracking process which comprises subjecting the oilto cracking conditions of temperature and superatmospheric pressure in aheating zone, discharging the heated oil into a vapor separating zone,removing vapors from said vapor separating zone and subjecting the sameto primary and secondary dephlegma- 4 some tion thereby forming primaryand secondary reflux condensates, combining at least a portion of saidprimary reflux condensate with the oil being subjected to crackingconditions in said heating mne, passing said secondary refluxcondensate-to a second heating zone independent of the first mentionedheating zone and there subjeoting the same to cracking conditions oftemperature and nsure, and then passing said secondary reflux condensatedirectly to said vapor separating zone without passage through saidfirst mentioned heating zone.

EDWARD W. ISOM.

